MOC2-1622
Support for Hypothesis
that Groundwater is Fluid
Source for Gullies

Clicking on the small images above, and the links listed below, provides access to details
about evidence, gathered by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC),
that liquid water may have flowed on the surface of Mars during the past 7 years.
These captioned materials accompany publication of results regarding present-day
impact cratering and gully activity on Mars in the 8 December 2006 issue of
Science.

The first two releases, regarding gullies in an unnamed crater in Terra Sirenum and another
in the Centauri Montes region east of the Hellas Basin, give the details about the “smoking gun” evidence that
change has occurred in two martian gully settings located in the southern hemisphere,
nearly on opposite sides of the planet. In both cases, “before” and “after” images
were acquired, documenting that these changes occurred between 2001 and 2005 in
the Terra Sirenum case, and 1999 and 2004 in the Centauri Montes case.

The third release describes other examples of rare, light-toned deposits found
in martian gullies elsewhere on the planet, but in these cases no “before” image
is available to indicate when the light-toned material was emplaced. These cases,
however, help identify sites that should be repeatedly imaged by cameras on current and
future Mars orbiting spacecraft, to see if any new light-toned flows occur.

The fourth release explains why the new light-toned gully deposits in the unnamed
craters in the Terra Sirenum and Centauri Montes regions cannot be the product of
downslope movement of dust. In other words, they are not the product of dry, granular
flow, but instead must have involved a fluid that has the physical properties of
liquid water. Key differences between light and dark slope streaks—generally
considered to have formed by mass movement of dust—and the
new gully deposits, are examined.

The fifth release centers on a related and important topic—the growing evidence
that martian gullies generally formed by erosion caused by fluids that seeped from the
ground. Evidence includes an important case in which a single gully formed at a site
where a fault intersects a crater wall; on Earth, groundwater preferentially flows
along cracks created by faulting and springs will result where the fault reaches
the planet’s surface.